In filling machines of said type, use has previously been made of a method which entails that, during the gas sterilisation stage, a sterilisation gas is supplied centrally in conjunction with the open end of the packages. The gas or gas mixtures supplied to the package is flowing down towards the inner region of the package whereby it returns back to the opening once it reaches the inner end of the package. Today the return flow is not taken care of. It comprises sterilised gas or gas mixture which uncontrolled spreads in the surrounding chamber and may cause flows of unsterilised gas to disturb an aseptic air flow barrier disposed downstream in the filling machine, which flow barrier is required in order not to jeopardise the aseptic level attained in the sterilisation zone.
An uncontrolled return flow is also troublesome when it comes to the possibilities of reusing the gas. This is particularly important when sterilisation gas is handled. If a more directed return flow could be achieved the unintentional spreading of the sterilisation gas in the aseptic chamber can be restricted to an even greater extent than previously, and it would then be easier to reuse the gas.
Further, for the filling operation, it is an advantage if the outside of the package could also be sterilised. This would minimise the risk of re-infection as it would secure that the surrounding flow will be directed from the opening of the package and not towards it. Otherwise there is a slight, but nevertheless tangible risk that microorganisms will, in an uncontrolled manner, re-infect the sterilised surface of the inside of the package.